pulp protection materials

how is pulp injury caused?

it is multifactorial in origin, so every effort should be taken to minimize such injuries

when is dental pulp subjected to injuries?

before, during and after restoration of carious tooth

when is the pulp subjected to injury before restoration?

carious lesion

when is the pulp subjected to injury during cavity preparation?

heat and desiccation

when is the pulp subjected to injury during insertion of restorative material?

1. by the pressure of condensation of amalgam or direct gold restoration

2. chemicals generated during setting can be harmful

3. the hydraulic pressure produced during cementation of the crown

when is the pulp subjected to injury after placement of restoration?

by oral conditions:

• microleakage

• thermal shock

• percolation

• galvanism

in normal conditions, what acts as a natural protectant of the pulp?

dentin, as it provides protection against thermal, chemical and bacterial stimuli as well as electric insulation

what is the best protective material to the pulp?

the natural healthy dentin

how does dentin provide mechanical protection?

vital dentin is a visco-elastic material that provides stress breaking action against any abnormal mechanical stresses

how does dentin provide thermal protection?

the heat dissipation upon the large surface area of dentin together with its fluid contents limits the thermal irritation to the pulp to be within its tolerance threshold

how does dentin provide chemical protection?

the buffering capacity of the dentinal fluid can neutralize any chemically irritant molecules from damaging the pulp tissue

how does dentin provide bacterial protection?

the dentinal tubules wavy course and the narrow diameter of the dentinal tubules at the DEJ and the continuous outflow of the dentinal tubules limits bacterial invasion to the pulp

why are lining materials used along permanent restorations?

the material used for permanent restorations may not be sufficient by itself to restore all of the lost protective functions of enamel and dentin, so, several lining materials are used to line the prepared cavities underneath permanent restorations as dentin substitutes to provide thermal, chemical, electric, mechanical and biological protection of the dentin-pulp organ as well as to medicate the pulp or to compensate for the lost esthetics

what do pulp protection materials protect against?

• thermal irritation due to conductivity of metallic restorations to thermal changes

• chemical irritation due to acids and monomers in nonmetallic restorations that may lead to pulpal damage and necrosis

• mechanical irritation due to force of condensation

what do some pulp protection materials do?

seal the cut dentinal tubules, while some others may enhance the deposition of calcific barrier on the pulpal surface of the cut dentinal tubules, or return the cavity depth in deep cavities to the conventional depth to be filled with amalgam and this will allow the equal distribution of forces

what is the ideal requirements of liners and bases?

1. must be nonirritant to the pulp

2. must be compatible with restorative material, i.e, not reacting with it or interfere with its setting reaction

3. strong enough to withstand the force of mastication and force of condensation

4. reduce the thermal conductivity of metallic restorations

5. improve marginal seal of restorative material and adaptation to cavity walls and margins

6. prevent chemical exchange between the restoration and the tooth

7. reduce galvanic action of certain metallic restorations

8. resist degradation in oral fluids

9. enhance the formation of reparative dentin

10. easy to be manipulated and applied

how to protect the pulp when dentin is lost due to caries?

by the use of intermediary bases

what are the intermediary bases?

these are materials placed between the restorations and the tooth structure to protect the vital pulp

what are the goals of intermediary bases?

to give protection to the pulp. they are not concerned with the resistance and retention features of the cavity and must be mechanically passive

what is varnish?

a material applied in thin film thickness not exceeding the leakage space at the restoration / interface. its film thickness is usually about 5-10 μm and it can be applied to all prepared cavities on both enamel and dentin

what is liner?

a material placed as thin coating and its main function is to provide barrier against chemical irritation, or as thermal insulators. it is applied only on dentin

what liners protect against chemical irritation?

• calcium hydroxide

• GIC

what liners protect against thermal insulators?

• GIC

• ZOE

what are bases?

thicker than a liner and acts as a substitute for lost dentin. it functions as a barrier against chemical, thermal and mechanical irritation and is only applied on dentin

classification of Intermediary Bases (Pulp Protection Materials)

• cavity sealers (cavity varnish and adhesive sealer)

• cavity liners

• sub-bases

• cement bases

what are cavity varnishers?

also known as solution liners, they are a sealing agent used as protective coatings on the freshly cut tooth structures, with a film thickness of 5-10 μm, which is less than the microleakage space. it has to be applied to all the prepared cavity walls, pulpal floor and the margins, either solo or in combination with the base

what is the compositon of cavity varnishers?

• copal resin (natural gum) or synthetic resin – 10%

• organic solvent, such as acetone, chloroform or ether is 90%

• copal rosin is dissolved in the ether and when the ether evaporates, a thin film of resin is left on the surface of the cavity

functions of cavity varnish

• it work as an insulator against chemical irritants by preventing the penetration of acid from the restorative material and by preventing the penetration of corrosion products from amalgam restoration

• it minimizes the marginal leakage around the restorations

• acts as a barrier against biological irritants with respect to its effect of minimizing the microleakage, the ingress of the bacteria into the microscopic space is also minimized

what are some disadvantages of cavity varnishers?

• not an effective thermal insulator even with 2-3 coatings

• very stick in nature

• solvent may dissolve the previous coats

• water soluble

what are indications for cavity varnish?

1. below amalgam restorations apply varnish to all the cavity walls, pulpal floor and to the margins

2. below zinc phosphate cement apply varnish to the pulpal floor and to prevent the acid penetration

what are contraindications for cavity varnish?

• composite resin restorations because the solvent in the varnish will react with resin and soften the resin and it also prevents proper wetting of the cavity walls by the resin

• glass ionomer cement as the varnish interferes with chemical adhesion property of the GIC cement

how is cavity varnish applied?

should be applied in thin consistency and if it is too viscous (thick) upon storage, it should be thinned by adding solvent. a viscous varnish will not wet the cavity wall and hence not effective in reducing microleakage. it is important to obtain uniform and continuous coating on the cavity surface. when the first layer dries, small holes / voids usually develops (55% sealed) a second or third application fills these voids and produces continuous coating.

how can varnish be applied?

by using a brush or a cotton pellet or disposable brush tips

what is dentin (adhesive sealer)?

recently, dentin bonding agents have been use to seal dentin tubules in place of cavity varnish

what are the indications for dentin (adhesive sealer)?

• treat or prevent hypersensitivity

• used instead of varnish

• seal the dentinal tubules

• ideal for use under all indirect restorations

what is the application process of the dentin sealer?

do not allow contact with soft tissue (HEMA and glutaraldehyde). apply the dentin sealer with the cotton-tipped applicator. apply over all areas of the exposed dentin

what are cavity liners?

also known as suspension liners, they are agents which are used as protective coatings on the freshly cut cavities and in addition they have therapeutic action on pulp

what is the thickness of cavity liners?

25 µm

what is the composition of cavity liners?

• therapeutic agent (CaOH, ZOE, F) which is dispersed or suspended in

• resin solution, which acts as a carrier, the solvent evaporates leaving a layer of calcium hydroxide or ZOE, on the cavity surface

what are some types of cavity liners?

• calcium hydroxide based

• ZOE based

• GIC liners

what are the advantages of calcium hydroxide based liners?

• helps in formation of reparative dentin or secondary dentin

• neutralizes acid

• mildly bactericidal

what are the disadvantages of calcium hydroxide based liners?

• highly soluble in oral fluids

• very poor strength

what are advantages of ZOE based cavity liners?

• acts as chemical barrier

• relieves the pulpal inflammation

• has palliative (abundant) effect

how is cavity liner applied?

the same as that of applying varnish, but is mandatory to remove the liner from margins of the cavity, as calcium hydroxide dissolves in the oral fluids and is not effective against microleakage

what are the indications of cavity liners?

• as a thermal insulator the liners are applied below permanent restorations such as amalgam

• help in healing pulp

• help in reparative dentin formation

• helps to sooth to the inflamed pulp

what are the contraindications of cavity liners?

ZOE liners are contraindicated below the composite resin restoration as it interferes with polymerization

what are glass ionomer liners?

GIC became popular as a liner in 1994. the choice of liner is modified GIC in the form of resin modified RMGIC

why is RMGIC the choice of GIC for liners?

due to:

• chemical adhesion

• good mechanical strength

• fluoride release

• well controlled setting time

• rapid achievement of strength

what is the sub-base?

therapeutic materials placed in deep portion of the cavity preparation with specific pharmacological action. they should be covered with supporting base as they have low strength

what is the most commonly used sub base?

calcium hydroxide

why does calcium hydroxide have to be covered by a strong base?

it has low mechanical property

when is calcium hydroxide cement used?

• used as direct and indirect pulp capping agent

• it can be used with composite resin as it does not interfere with polymerization

• used in extremely deep areas as an antibacterial agent

• can be used as a cavity liner, a sub base or a base if high strength

what are the forms of the calcium hydroxide cement?

• 2 paste system

• light cured single paste system

what are the properties of calcium hydroxide?

• it has low mechanical properties

• it has low compressive strength, hence, it cannot withstand condensation forces

• it stimulates the formation of reparative dentin because of its alkaline pH (11.7)

what is pulp capping?

the procedure of placing the calcium hydroxide cement onto the injured pulp to allow it to heal

what are the types of pulp capping?

• direct

• indirect

what is indirect pulp capping?

the procedure in which calcium hydroxide cement is placed on the deepest portion of the cavity where this is no pulpal exposure

what is direct pulp capping?

the procedure of placement of calcium hydroxide directly on the exposed healthy pulp to allow it to heal and repair

what are cement bases?

a layer of cement that is placed under the permanent restoration to protect the pulp against numerous types of irritation, such as thermal and chemical irritation

cement bases are a replacement for what?

protective dentin, which has been destroyed during caries process or during cavity preparation or both. it is typically 0.5-1 mm in thickness

what are some examples of bases?

1. zinc phosphate cement

2. zinc oxide eugenol (modified)

3. zinc poly carboxylate cement

4. glass ionomer

5. hard setting calcium hydroxide

what are bases used for?

• as a chemical insulator

• as a thermal insulator

• as mechanical support for the restoration by distributing stresses to the underlying dentin

• this mechanical support provides resistance against fracture of dentin during condensation of amalgam

what are the thermal properties of cement bases?

the minimum thickness of the base necessary to provide adequate thermal insulation is 0.75 mm. all bases generally have thermal insulating properties

what are the chemical barrier of cement bases?

all cement bases are effective in protecting pulp against chemical irritants

what must be done if zinc phosphate cement is applied as a thermal insulator?

cavity varnish has to be applied first to the cavity walls and floor before base placement as the acid from the cement can penetrate and irritate the pulp

what must be done if GIC is applied as a base?

the deep areas in the cavity should be protected by calcium hydroxide cement as a sub-base

what is the strength of cements like?

if it is used as a base should have sufficient strength to withstand the forces of condensation so that the base is not fractured during insertion of the restoration. it should also withstand fracture or distortion under any masticatory stress transmitted through restoration

what is the strongest cement base?

zinc phosphate cement, but the strength of the other cement bases is sufficient to withstand condensation pressure of restorative material

clinical considerations for pulp protection materials

• remaining dentin thickness (RDT)

• design of the cavity

• adhesive property of the material

• proximity of the pulp to the cavity floor

• type of restorative material used

in deep cavities where maximum protection against all types of insults is required, what may be needed?

a varnish and base

what are some different bases used under amalgam restorations?

• if the cavity is shallow, only a cavity varnish is needed

• if moderately deep cavity, zinc phosphate or zinc polycarboxylate or GIC is needed

• if deep cavity, calcium hydroxide and ZOE are effective as sub base, place strong base over this

what are some different bases used under composite restorations?

• cavity varnish, ZOE formulated liners and ZOE base materials are contraindicated as it interferes with polymerization

• GIC is the preferred base material

ZOE cement

• it is dispersed in powder and liquid form

• the pH is near &, thus it is the least irritating of all the cements

• most often used as temporary restorative material

• the conventional cement is relatively weak, hence, reinforced ZOE have been introduced

how is ZOE been reinforced?

by the addition of products like:

• polymer

• hydrogenated rosin / resin

• by the surface treatment of ZOE powder particles

what are the advantages of ZOE?

• soothing / sedative effect on pulp

• thermal insulating base if reinforced type

• palliative effect upon dental pulp

what are the disadvantages of ZOE?

• low strength in conventional ZOE

• not compatible with all restorative materials

zinc phosphate cement

• it is also in dispensed in powder and liquid form

• hard and strong but irritating to the pulp

what is the zinc phosphate cement used for?

• as a thermal insulator

• protect against mechanical trauma

what are the advantages of zinc phosphate cement?

• provides good protection against thermal shock

• because of its high compressive strength it can withstand mechanical trauma during condensation of restorative material

what are the disadvantages of zinc phosphate cement?

irritating to the pulp as it is highly acidic, so cavity varnish is necessary before base is applied

zinc polycarboxylate cement

• dispensed as powder and liquid

• the powder is similar to zinc phosphate cement

what are uses of zinc polycarboxylate cement?

• acts as a protective barrier against thermal shock

• acts as protective barrier against chemical insult

what are the advantages of zinc polycarboxylate cement?

• it has potential for chemical adhesion to the calcium ions in enamel and dentin

• anti-cariogenic property because of release of fluoride ions

what are the two types of glass ionomer cement?

1. convention powder, liquid system

2. light cured glass ionomer could be single paste system or power:liquid system

what are the advantages of GIC?

• the primary purpose of GI liner is to serve as an intermediate bonding material between tooth and composite restoration

• reduces the gap caused during polymerization shrinkage

• proven chemical adhesion to the tooth structure

• anti cariogenic property, its fluoride release property increases the resistance to caries

why is GIC biocompatible with the pulp?

• it has a high molecular weight

• the polymeric nature of polyacrylic acid (weak acid)

what is the sandwich technique?

in which composite resin is bonded to the glass ionomer liner. the advantage of both materials is met (advantages of GIC + esthetic property of composite restoration.) GIC serves as dentin bonding agent, as a result of its adhesion to dentin, GIC tends to reduce the gap formation at the interface between tooth restoration caused by polymerization shrinkage of composite resin